Semiconductor devices are becoming smaller and more dense with the evolution of new technology. However, increases in circuit density produce a corresponding increase in overall requirements for semiconductor devices. Manufacturers of semiconductor devices in order to remain competitive are therefore constantly challenged to improve their products. This is done in a number of different ways, such as, for example, by identifying and eliminating defects or to produce features that give the manufacturer a competitive advantage.
Whereas significant improvements have been made to eliminate systematic defects by reducing process variability. Process improvements alone are not sufficient, and therefore new techniques have to be employed to improve the products.
Furthermore, in printed circuit board manufacturing, the testing of the accurate connection of electrical and electronic components on the printed circuit board is an important part of the process if high quality products are to be produced. With certain types of components, the correct placement and connection is critical in order to avoid damage to the circuit. For example, the improper installation of surface mounted polarized capacitors, e.g. electrolytic or tantalum capacitors, on electronic circuit board or board assemblies poses a potential safety hazard, such as, for example, explosion or fire.
For such electronic components, such as, capacitors, it is therefore crucial to ensure not only that good electrical connection is achieved, but also that the electronic component or capacitor is correctly oriented (i.e., correctly polarized) with respect to the connector pads on the circuit board.
Reversing the electronic component or capacitor on a circuit board can happen even on an automated line where capacitors come out of pre-packed tape reels. If a severed tape reel needs to be reconnected, there is always the possibility of incorrect loading.
Visual inspection for the correct polarization of such capacitors is time consuming and costly and may even be impracticable in cases where the capacitor is positioned underneath another component.
An alternative to visual inspection involves the vibration or shaking of the assembly to verify that no capacitor is loose. However, this technique does not indicate whether the orientation of the capacitor is correct.
Other more sophisticated testing techniques have been developed for detecting reversed polarized capacitors, but these techniques require the use of complex and expensive test apparatus.
Other known techniques for ensuring correct placement and orientation of electronic components have been disclosed, such as, for example, in IBM Technical Disclosure Bulletin, entitled "Polarized Capacitor Mounting", Vol. 28, No. 3, pp 940-41 (August 1985), or in IBM Technical Disclosure Bulletin, entitled "Two-Pad Surface-Mounted Tantalum Chip Capacitor With Diagonally Opposed Contacts", Vol. 31, No. 3, pp 367-368 (August 1988). These additional techniques are not necessarily suitable for surface mount capacitors.
While the above referenced techniques may achieve the required result, some do not address the additional problem arising when repairs are carried out to a circuit board after the manufacturing and testing process. When polarized capacitors are replaced during a repair, it is fairly uncommon for additional testing to be carried out on the new capacitor. The aforementioned safety hazard will then be present in the repaired circuit board if the capacitor is reversed.
U.S. Pat. No. 5,010,447 (Wallace), discloses a method for testing for the proper electrical and mechanical connection of a capacitor to a printed circuit board by placing the capacitor terminal in series with a power lead for a memory device by splitting one of its bonding pads into two separate pads, electrically isolated form one another. An electrical test confirming power to the memory device confirms the proper mechanical and electrical connection of the capacitor terminal to its pair of bonding pad parts. This technique is not capable of determining the proper orientation of a device such as a polarized capacitor and cannot therefore provide protection against the hazards posed by the improper placement of such a device.
An improved technique which provides such protection in a cost-effective manner is therefore required.
Accordingly, the present invention provides an arrangement for surface mounting an electrical component on a circuit board, the arrangement being testable electrically to indicate both the proper mechanical mounting and the correct orientation of the component on the circuit card, the arrangement comprising: an electrical component including first and second power connector leads, and further including a test connector lead; a circuit board including a connector footprint having first and second pads connected to supply rails on the board and also a pair of test pads connected to first and second test points on the card; wherein when the component is properly connected and oriented with respect to the connector footprint, the test lead is connected to a first of the test pads and one of the first or second power leads bridges between the second test pad and one of the pair of pads connected to the supply rails; and wherein improper connection and orientation of the component is indicated when said one of said first or second power leads bridges between the first of the test pads and the other of the pair of pads connected to the supply rails.
In a preferred arrangement, the component is a polarized capacitor, in particular a tantalum capacitor.
The arrangement according to the invention allows for automatic checking of the presence and orientation of the device at the test operation and does not require visual inspection--either manual or automated. The present invention also avoids the need to use expensive fused capacitors.
A preferred embodiment of the invention will be described by way of example only with reference to the accompanying drawings.